1. Field of the Invention
The present invention relates to a master carrier for magnetic transfer carrying information that is transferred magnetically to a slave medium.
2. Description of the Related Art
In a magnetic transfer method, the surface of the substrate of a master carrier, coated with a magnetic material having a “land/groove” pattern that corresponds to information to be transferred, is brought into intimate contact with the surface of a slave medium having a magnetic recording portion. In this state, a transfer field is applied, and a magnetization pattern corresponding to information (for example, a servo signal) carried by the master carrier is transferred and recorded on the magnetic recording portion of the slave medium. Such a magnetic transfer method is disclosed, for example, in Japanese Unexamined Patent Publication Nos. 63(1988)-183623, 10(1998)-40544, and 10(1998)-269566.
The master carrier that is used for magnetic transfer is constructed of a silicon substrate, a glass substrate, or the like. The substrate has a land/groove pattern formed with a magnetic material by photolithography, sputtering, etching, etc.
It is also possible to generate the aforementioned master carrier by utilizing the lithography being used for semiconductor device fabrication or the stamper generation technique being used to generate an optical disk stamper.
To enhance the quality of transfer in the aforementioned magnetic transfer method, it is extremely important to bring the master carrier and the slave medium into direct contact with each other without a gap. If the contact between the two is poor, regions where magnetic transfer is not performed will occur. If magnetic transfer is not performed, missing signals occur in the magnetic information transferred to the slave medium and therefore the signal quality is reduced. In the case where a signal recorded is a servo signal, the tracking function cannot be sufficiently obtained, and consequently, there is a problem that reliability will be reduced.
In addition, in the magnetic transfer method disclosed in Japanese Unexamined Patent Publication No. 11 (1999)-117800, a magnetic recording medium is magnetized in advance in one direction. Thereafter, a master carrier with a soft magnetic layer is brought into direct contact with the magnetic recording medium, and a transfer field is applied in the opposite direction. In this way, more satisfactory transfer is made possible.
In the aforementioned master carrier, incidentally, it has been found that in the case where the land/groove pattern on the substrate corresponding to transfer information is formed from a magnetic material, the shape of the top of each land in the land/groove pattern has influence on a transfer characteristic.
As indicated in experiments to be described later, a plurality of different master carriers were generated, magnetic transfer was performed on a slave medium by employing the master carriers, and the quality of transferred signals was confirmed. As a result, it has been found that there are cases where depending on the generating condition for the master carrier, the signal quality is inferior to the signal quality in the case of a conventional method in which signals are recorded directly on the slave medium by a magnetic head, etc.
After the confirmation of the shape of the land/groove pattern on the master carrier, it has been found that the flat shape of the corner of each land in the land/groove pattern has a great influence on signal quality. For example, in the case of slave disk medium, a land/groove pattern for information corresponding to a servo signal has a plurality of rectangular or square lands elongated in the direction of the track width (radial direction). In this case, it has been found that if each of the 4 corners is formed at right angles without being chamfered, it chips when the master carrier is repeatedly brought into direct contact with the slave medium. It has also been found that the chipped corner produces dust particles which will cause the quality degradation of transferred signals.
Judging from the fact mentioned above, it is necessary to chamfer the corners of each land of the land/groove pattern. However, it has been found that in the case where the corner is chamfered into the shape of a circular arc, the magnitude of the radius of the rounded corner has influence on the quality of transferred signals. That is, master carriers with a different rounded corner were generated and various experiments were made with respect to the radius of the rounded corner having influence on signal quality. As a result, it has been found that if the radius R of the rounded corner is increased, the rounded corner causes recording loss to occur in a transfer field applied when magnetic transfer is performed with the master carrier and the slave medium held in direct contact with each other. Because of this, the magnetization pattern formed on the slave medium becomes incomplete, and distinct signals cannot be recorded.
If the radius R of the rounded corner is reduced, recording loss is reduced and therefore the quality of transferred signals is enhanced. In this case, if magnetic transfer is performed a plurality of times by using the master carrier, signal quality is reduced. From this fact it has been found that (1) the corner of the land in the land/groove pattern chips, (2) the chipped pieces remain on the land/groove pattern, and (3) missing signals occur due to poor magnetic transfer.
Particularly, if the storage capacity of the slave medium is increased, the lands and grooves in the land/groove pattern on the master carrier become finer. Because of this, reliability must be enhanced while ensuring the compatibility between the conflicting requirements of the prevention of damage to the land corners in the land/groove pattern and the reduction in recording loss.
The present invention has been made in view of the problems mentioned above. According, it is an object of the present invention to provide a master carrier for magnetic transfer which is capable of enhancing the quality of transferred signals by a reduction in recording loss, also enhancing durability by the prevention of damage to a land/groove pattern formed on the master carrier, and preventing poor magnetic transfer, when performing magnetic transfer by applying a transfer field to the master carrier and the slave medium being held in direct contact with each other.
In addition, in the aforementioned magnetic transfer, dust particles have to be removed at a high level, because one or two flat master carrier are brought into direct contact with one side or both sides of a slave medium. If dust particles are present on the intimate contact portion, stable magnetic transfer cannot be performed and, in addition, there is a possibility that the master carrier or slave medium itself will be damaged.
In the magnetic transfer, relatively strong pressure is applied on the master carrier and the slave medium to perform whole-surface contact. Because of this, if magnetic transfer is repeated a large number of times, and the number of intimate contacts is increased, the soft magnetic layer formed on the substrate is separated in this step. The separated portion on the intimate contact portion reduces the quantity of transferred signals and degrades the durability of the master carrier.
Based on the result of an analysis performed on the separated portion of the soft magnetic layer, it has been found that the master carrier is considerably deformed during the intimate contact between the master carrier and the slave medium, and that separation of the soft magnetic layer occurs particularly at a place where the amount of deformation is great.
Furthermore, in the magnetic transfer, relatively strong pressure is applied on the master carrier and the slave medium, and in the whole-surface contact state, a transfer field is applied. Thereafter, the master carrier and the slave medium are mechanically separated from each other, or pressurized air is introduced through the outer circumferential portion between the master carrier and the slave medium to separate them from each other. Next, the master carrier and the slave medium are moved away from each other by vacuum suction. Because of this, if magnetic transfer is repeated a great number of times, the magnetic layer formed on the substrate will undergo wear, abrasion, separation, chipping, and edge deformation during the aforementioned steps. Consequently, there is a problem that (1) the shape of a pattern to be transferred will change and the quality of transferred signals will be reduced, (2) wear powder on the intimate contact portion will cause missing signals and reduce the quality of transferred signals, and (3) the durability of the master carrier will be degraded.
More specifically, the magnetic layer formed on the “lands” on the substrate of the master carrier becomes thinner due to wear and abrasion, or is separated from the substrate. In addition, the edge of the magnetic layer chips and the magnetic layer becomes narrower. Furthermore, dust particles adhere to the direct contact portion between the magnetic layer and the slave medium and cause scores to occur in the magnetic layer. Thereafter, poor contact occurs between the master carrier and the slave medium. Thus, it becomes difficult to perform stable magnetic transfer repeatedly.
The present invention has been made in view of the problems mentioned above. Accordingly, another object of the present invention is to provide a master carrier for magnetic transfer which is capable of preventing the wear, abrasion, separation, chipping, edge deformation, etc., of the magnetic layer, also enhancing durability, and preventing poor transfer, when performing magnetic transfer by applying a transfer field with the master carrier and the slave medium held in direct contact with each other.
In addition, in the magnetic transfer method mentioned above, the influence of a demagnetizing field on the magnetic recording medium is slight because of the application of a static field, as compared with a conventional servo write operation which is performed using a magnetic head. However, in the case where a transfer field is applied after the initial DC magnetization of a magnetic recording medium, as in a magnetic transfer method disclosed in Japanese Unexamined Patent Publication No. 11(1999)-117800, there is a need to take the influence of a demagnetizing field on the magnetic layer of the magnetic recording medium into consideration. In recording media for longitudinal magnetization, there is a tendency for a magnetization transition region interval to shorten to meet the high-density requirement of storage capacity. In recording media in which the magnetization transition region interval has shorten, there are cases where because of the influence of a demagnetizing field during magnetic transfer, a shift will occur between a pattern on a master carrier for magnetic transfer and a magnetization pattern on a magnetic recording medium that is recorded according to the pattern of the master carrier. That is, there are cases where a desired magnetization pattern cannot be recorded accurately on a magnetic recording medium and therefore each magnetization transition region will be shifted from its original position.
The shift of the magnetization transition place, that is, the shift of a magnetization pattern from its original position will have a great influence on the accuracy of recording and reproduction that are performed through a magnetic recording medium. Particularly, in the case where information to be transferred is a servo signal, tracking performance is reduced and reliability is reduced.
The present invention has been made in view of the circumstances mentioned above. Accordingly, still another object of the present invention is to provide a master carrier for magnetic transfer that is capable of recording a desired magnetization pattern on a magnetic recording medium with a high degree of accuracy.